Patent Literature 1 describes an electric-discharge machining apparatus that detects a gap state with respect to each of machining pulses applied to a machining gap by a check pulse in an initial stage. Specifically, a check-pulse generation circuit generates the check pulse after a delay by a time period during which a switch-on start signal is output and the electrode gap voltage becomes sufficient for electric discharge. A gap-state determination circuit compares the detection voltage of the machining gap with a reference voltage only during a generation period of the check pulse, so as to determine the presence of occurrence of an abnormality such as sustained arc discharge or a short circuit. With this configuration, according to Patent Literature 1, when an abnormality such as a sustained arc discharge or a short circuit has occurred, the abnormality is eliminated, and normal electric discharge is generated within a short time thereafter. Accordingly, the frequency of the normal electric discharge can be increased, and the machining speed can be increased.
Patent Literature 2 describes an electric-discharge machining apparatus that applies an alternating current (AC) voltage to an electrode gap only during a pause time of the pulse voltage application, in order to detect the degree of insulation of the insulating machining fluid present in the electrode gap. With this configuration, according to Patent Literature 2, the true factor of electric-discharge concentration is detected without detecting the deterioration of the degree of insulation due to field metal ions, which are not the factor in electric-discharge concentration, to perform abnormality determination in the electrode gap by comparing the detection result with a reference value. When an abnormality is detected, control is executed to recover a state of the electrode gap, and thus machining speed does not decrease.
Patent Literature 3 describes an electric-discharge machining apparatus set with an idle time between rough machining in which a rough-machining power supply is energized to apply a machining voltage to a load unit to perform cutting and finish machining in which a high-frequency finishing power supply is energized to apply the machining voltage to the load unit to perform surface finishing. With this configuration, according to Patent Literature 3, a voltage can be applied between machining electrodes after impedance between the machining electrodes is recovered during the idle time, thereby enabling machining to be performed efficiently.